Fujino K, Koyano K, Ohmori H
Department of Physiology, Faculty of Medicine, Kyoto University, Sakyo-ku, Japan.
J Neurophysiol. 1997 May;77(5):2788-804. doi: 10.1152/jn.1997.77.5.2788.
Electrical properties of cochlear efferent (olivocochlear) neurons were investigated with the use of the whole cell patch recording technique in slice preparations of the neonatal rat (postnatal days 5-11). Lateral and medial olivocochlear (LOC and MOC, respectively) neurons were retrogradely labeled with a fluorescent tracer injected into the cochlea. Stained neurons were identified under a fluorescence microscope, and they were subjected to whole cell recording. LOC and MOC neurons showed different electrophysiological properties. Both showed spike trains of tonic pattern in response to injection of depolarizing current pulses at the resting membrane potential (-60 to -70 mV). However, when the membrane was slightly hyperpolarized (-72 to -76 mV), LOC neurons showed spike trains with a long first interspike interval (ISI), whereas MOC neurons showed spike trains with a long latency to the first spike. Extracellular application of 4-aminopyridine (4-AP; 0.5-2 mM) shortened these ISIs and latencies. In voltage-clamp experiments, two transient outward currents with different (fast and slow) decay kinetics were observed in LOC neurons. The fast outward current (I(A-LOC)) was inactivated by the preceding depolarization, and decayed with a time constant (tau) of 86 ms (at 0 mV). The preceding potential, which reduced the current size to the half-maximum (V1/2), was -72 mV. The slow current (I(KD)) decayed with a tau of 853 ms (at 0 mV). I(A-LOC) was sensitive to 4-AP (2 mM), and was less sensitive to tetraethylammonium chloride (TEA; 20 mM). I(KD) was partially blocked by TEA (20 mM), but was insensitive to 4-AP (2 mM). The recovery from inactivation of I(A-LOC) was time dependent with a time constant (tau(rec)) of 32 ms at -90 mV. MOC neurons also showed a transient outward current that consisted of a single transient component (I(A-MOC)) with a steady outward current. I(A-MOC) was inactivated by the preceding depolarization. Decay tau of I(A-MOC) was 33 ms (at 0 mV), and V1/2 was -75 mV. I(A-MOC) was sensitive to 4-AP (0.5-1 mM). The time-dependent recovery from inactivation of I(A-MOC) was faster than that of I(A-LOC), and tau(rec) was 15 ms at -90 mV. The different kinetics of transient outward currents between LOC and MOC neurons seems to be responsible for the difference in firing properties of these two neurons.
采用全细胞膜片钳记录技术，在新生大鼠（出生后5 - 11天）的脑片标本中研究了耳蜗传出（橄榄耳蜗）神经元的电特性。分别向耳蜗注射荧光示踪剂，逆行标记外侧和内侧橄榄耳蜗（分别为LOC和MOC）神经元。在荧光显微镜下识别染色的神经元，并对其进行全细胞记录。LOC和MOC神经元表现出不同的电生理特性。在静息膜电位（-60至-70 mV）下，向细胞内注射去极化电流脉冲时，二者均表现出紧张型的动作电位发放。然而，当细胞膜轻微超极化（-72至-76 mV）时，LOC神经元的动作电位发放具有较长的首个峰峰间期（ISI），而MOC神经元的动作电位发放则具有较长的首个峰潜伏期。细胞外施加4 - 氨基吡啶（4 - AP；0.5 - 2 mM）可缩短这些ISI和潜伏期。在电压钳实验中，在LOC神经元中观察到两种具有不同（快和慢）衰减动力学的瞬时外向电流。快速外向电流（I(A-LOC)）在先前的去极化作用下失活，在0 mV时以86 ms的时间常数（tau）衰减。使电流大小降至最大值一半时的前一个电位（V1/2）为-72 mV。慢电流（I(KD)）在0 mV时以853 ms的时间常数衰减。I(A-LOC)对4 - AP（2 mM）敏感，对氯化四乙铵（TEA；20 mM）不太敏感。I(KD)被TEA（20 mM）部分阻断，但对4 - AP（2 mM）不敏感。在-90 mV时，I(A-LOC)从失活状态恢复的时间常数（tau(rec)）为32 ms，呈时间依赖性。MOC神经元也表现出一个瞬时外向电流，该电流由一个单一的瞬时成分（I(A-MOC)）和一个稳定的外向电流组成。I(A-MOC)在先前的去极化作用下失活。I(A-MOC)在0 mV时的衰减tau为33 ms，V1/2为-75 mV。I(A-MOC)对4 - AP（0.5 - 1 mM）敏感。I(A-MOC)从失活状态恢复的时间依赖性比I(A-LOC)快，在-90 mV时tau(rec)为15 ms。LOC和MOC神经元之间瞬时外向电流的不同动力学似乎是这两种神经元放电特性差异的原因。
